The invention relates to a system for monitoring the closing of a movable barrier mounted on a frame surrounding an opening and movable back and forth relative thereto between an open state and a closed state, with a first circuit provided outside of the movable barrier for the purpose of emitting a signal indicating the closing state.
Systems of this kind are needed chiefly in vehicles, e.g., in streetcars, trains or subways, to supervise the closing state of doors which have to be operated by remote control from a central point, such as a driver's cab.
Usually the barriers or doors in question are single-leaf sliding doors or doors having two leaves which can slide against one another, which can be driven back and forth in separate frames around the door openings of the passenger compartments by electrical, pneumatic or other actuators. Nevertheless, other kinds of doors may be involved, such as folding doors or swinging doors, as well as other movable barriers such as windows, flaps, sliding valves or the like. [For the sake of simplicity, however, the word "door" will be used herein to refer to all kinds of such movable barriers.]
The door states which are to be signaled are especially the "open" state or "closed" state, and the state of being free to close. This is to be understood to mean that a door is able to close or is in the "free" state if it can be moved to a closed position by the actuator. On the other hand, a door is not closable or is in the "blocked" state when some obstacle, such as a passenger, a box or the like, is blocking the opening and the door therefore cannot be fully closed by operating its actuator.
The states of "open" or "closed" are usually monitored by means of electromechanical limit switches which are actuated when the doors approach their closed positions. These limit switches are disposed on the frame and connected to circuits which emit a signal identifying the "open" or "closed" state and thus indicate the state of the door to the driver of a vehicle or produce a controlling signal. The circuits are disposed outside of the doors, i.e., they are mounted not on the latter but on the frame or other part of the vehicle or the like and therefore are stationary, in contrast to the doors, and can be moved only together with the vehicle or the like.
The presence of an obstruction in the opening might be indicated by monitoring that period of time which is started in the closing operation by actuating the door driver. If one of the signals from the limit switches identifying the "closed" state does not arrive within a predetermined period of time after the actuation of the driver, this signifies that the door in question is in the "blocked" state on account of an obstruction.
Since such systems are often considered to be insufficiently safe, they can have, in addition to the limit switches, a switching means contained within the door itself which responds when the door encounters an obstruction and thereby supplies additional "free" o "blocked" signals which indicate an obstruction or trigger a controlling operation immediately without any predetermined waiting period.
One problem with such means of detection lies in their sensitivity to trouble and hence their insufficient reliability in operation. Their limit switches are subject to considerable mechanical wear, and in extreme cases their position in relation to the doors can change, which would falsify the "open" and "closed" signals. Furthermore, the switch means mounted on the doors themselves are connected to the circuits and indicator mounted outside of the doors by trailing electrical or pneumatic lines which are undesirable for safety reasons. SYstems of this kind therefore require careful maintenance that has to be performed repeatedly at frequent intervals of time.
The purpose of the invention is to construct the system of the kind described above such that the signals necessary for the indication of the closing operation and of the closing state of the door are produced without contact, i.e., without mechanical contact by physical components and without galvanic connections between the doors and the circuits provided outside of the doors.